core: implement basic policying support, fix #370

Implement mempool and consensus block creation policies, almost the same as
SimplePolicy plugin for C# node provides with two caveats:
 * HighPriorityTxType is not configured and hardcoded to ClaimType
 * BlockedAccounts are not supported

Other than that it allows us to run successfuly as testnet CN, previously our
proposals were rejected because we were proposing blocks with oversized
transactions (that are rejected by PoolTx() now).

Mainnet and testnet configuration files are updated accordingly, but privnet
is left as is with no limits.

Configuration is currently attached to the Blockchain and so is the code that
does policying, it may be moved somewhere in the future, but it works for
now.

config/config.go

@@ -46,7 +46,7 @@ type (
 		AddressVersion          byte      `yaml:"AddressVersion"`
 		SecondsPerBlock         int       `yaml:"SecondsPerBlock"`
 		LowPriorityThreshold    float64   `yaml:"LowPriorityThreshold"`
-		MaxTransactionsPerBlock int64     `yaml:"MaxTransactionsPerBlock"`
+		MaxTransactionsPerBlock int       `yaml:"MaxTransactionsPerBlock"`
 		MemPoolSize             int       `yaml:"MemPoolSize"`
 		StandbyValidators       []string  `yaml:"StandbyValidators"`
 		SeedList                []string  `yaml:"SeedList"`
@@ -59,6 +59,13 @@ type (
 		FreeGasLimit util.Fixed8 `yaml:"FreeGasLimit"`
 		// SaveStorageBatch enables storage batch saving before every persist.
 		SaveStorageBatch bool `yaml:"SaveStorageBatch"`
+		// Maximum number of low priority transactions accepted into block.
+		MaxFreeTransactionsPerBlock int `yaml:"MaxFreeTransactionsPerBlock"`
+		// Maximum size of low priority transaction in bytes.
+		MaxFreeTransactionSize int `yaml:"MaxFreeTransactionSize"`
+		// FeePerExtraByte sets the expected per-byte fee for
+		// transactions exceeding the MaxFreeTransactionSize.
+		FeePerExtraByte float64 `yaml:"FeePerExtraByte"`
 	}
 
 	// SystemFee fees related to system.